Consolidated Statements of Changes in Stockholders' Equity / Member's Interest - USD ($) $ in Thousands	Total	Common Class A	Common Class B	Accumulated Earnings/Deficit	Accumulated Other Comprehensive Income (Loss)	Common Stock Common Class A	Common Stock Common Class B	Additional Paid-in Capital	Noncontrolling Interest	Summit Materials, LLC	Summit Materials, LLC Members' equity	Summit Materials, LLC Accumulated Earnings/Deficit	Summit Materials, LLC Accumulated Other Comprehensive Income (Loss)
Beginning balance stockholders' equity at Dec. 30, 2017	$ 1,271,721			$ 95,833	$ 7,386	$ 1,104	$ 0	$ 1,154,220	$ 13,178
Beginning balance stockholders' equity (in shares) at Dec. 30, 2017						110,350,594	100
Beginning balance members' interest at Dec. 30, 2017										$ 1,291,594	$ 1,359,760	$ (51,031)	$ (17,135)
Increase (Decrease) In Stockholders' Equity [Rollforward]
Net contributed capital										15,615	15,615
Net income	36,330			33,906					2,424	63,837		63,837
LP Unit exchanges (in shares)						254,102
LP Unit exchanges	0					$ 2		929	(931)
Other comprehensive income (loss), net of tax	(4,903)				(4,705)				(198)	(6,481)			(6,481)
Distributions										(2,569)	(2,569)
Stock option exercises (in shares)						863,898
Stock option exercises	15,616					$ 9		15,607
Share-based compensation	25,378							25,378		25,378	25,378
Distributions from partnership	(69)								(69)
Shares redeemed to settle taxes and other (in shares)						190,333	1
Shares redeemed to settle taxes and other	(1,928)					$ 2		(1,930)		(1,943)	(1,943)
Ending balance stockholders' equity at Dec. 29, 2018	1,342,145			129,739	2,681	$ 1,117	$ 0	1,194,204	14,404				(23,616)
Ending balance stockholders' equity (in shares) at Dec. 29, 2018		111,658,927				111,658,927	99
Ending balance members' interest at Dec. 29, 2018										1,385,431	1,396,241	12,806	(23,616)
Increase (Decrease) In Stockholders' Equity [Rollforward]
Net contributed capital										19,076	19,076
Net income	61,123			59,066					2,057	88,597		88,597
LP Unit exchanges (in shares)		185,861				185,861
LP Unit exchanges	0					$ 2		971	(973)
Other comprehensive income (loss), net of tax	$ 2,645				767				1,878	2,645			2,645
Distributions										(2,500)	(2,500)
Stock option exercises (in shares)	1,065,446	1,065,446				1,065,446
Stock option exercises	$ 19,076					$ 11		19,065
Share-based compensation	20,403							20,403		20,403	20,403
Shares redeemed to settle taxes and other (in shares)		399,151				399,151	0
Shares redeemed to settle taxes and other	(619)					$ 4		(623)		(502)	(502)
Ending balance stockholders' equity at Dec. 28, 2019	1,444,773			188,805	3,448	$ 1,134	$ 0	1,234,020	17,366				(20,971)
Ending balance stockholders' equity (in shares) at Dec. 28, 2019		113,309,385	99			113,309,385	99
Ending balance members' interest at Dec. 28, 2019										1,513,150	1,432,718	101,403	(20,971)
Increase (Decrease) In Stockholders' Equity [Rollforward]
Net contributed capital										1,043	1,043
Net income	141,240									120,737		120,737
LP Unit exchanges (in shares)		376,487
Other comprehensive income (loss), net of tax	1,813									2,388			2,388
Distributions										(2,500)	(2,500)
Stock option exercises (in shares)		54,517
Share-based compensation										28,857	28,857
Shares redeemed to settle taxes and other (in shares)		650,206
Shares redeemed to settle taxes and other										(907)	(907)
Ending balance stockholders' equity at Jan. 02, 2021	$ 1,616,268			$ 326,772	$ 5,203	$ 1,145	$ 0	$ 1,264,681	$ 18,467				(18,583)
Ending balance stockholders' equity (in shares) at Jan. 02, 2021		114,390,595	99			114,390,595	99
Ending balance members' interest at Jan. 02, 2021										$ 1,662,768	$ 1,459,211	$ 222,140	$ (18,583)